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| Topic: | Local TV & BDU Misinformation Ad Campaigns This thread has 21 replies. Displaying posts 16 through 22. |
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| Post 16 made on Friday October 30, 2009 at 20:45 |
hd fan Regular Member |
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Posts: | March 2006
270 |
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I respectfully disagree with you on the 25% number. I beleive , note that I used the word beleive as I am not 100% sure that the number is around 1%, of course for a comparison between an NTSC transmition vs an ATSC signal on the same frecuency.
NTSC broadcasts need a 40 dB C/N ratio to be noise free. A 0 dBmV (1 mV @ 75 ohms) video signal is enough for a good picture without noise. The digital ATSC signal only needs 20 dB C/N or in other words the video carrier could go down to -20 dBmV. Less than that but above 15 dB C/N you see dropouts and problems. Below -25 dBmV or 15 dB C/N and the receiver is unable to decode and keep the lock.
So we know that there is a gap of 20 dB between both C/N values. Power levels go down by half for every -3 dB , therefore in -20 dB you have almost 7 , -3 dB's steps (7 times 3 dB equals 21 dB). If you divide 100 by 2 , seven times , you will get 0.78% and since it is acctually 20 dB not 21 dB then the exact value is actually 1.04%.
Therefore for CFTO who will eventually use the same frecuecy, CH 9, the EIRP level could go down to just 1% and theoretically still cover the same area. Other factors such as terrain will influence multipath and the final result will see some people loosing reception where before they use to have it. The actual value of 0.9% is very close to the theoretical limit.
Comparisons like in your list for the other Canadian TV stations is not fair since it does not take into consideration that the other stations are changing frecuencies therefore the 1% value does not apply. To cover the same area using higher frecuencies you requiere more power even when using the same modulation squeme or if you prefer TV standard.
For example City TV goes from 57 to 51 therefore inherently requieres less power when using the same format. The same applies to the rest of the pack. As a matter of fact since they are either staying on the same frecuency or going lower they could easily just broadcast 1% of the previous analog EIRP power value and still cover the same area.
CBLT goes from ch 5 to ch 20 therefore needs to increase power if using the same format but since it goes to digital it acctualy could reduce power.
As you can see on your list , except with CFTO , the rest are acctually planning to cover a larger area with the digital signal which is good news for potential viewers outside the previous analog coverage area.
When planning all this, engineers from Industry Canada, take into considerations other factors , such as protection from/with other services and to avoid interference with nearby stations either co-channel or adjacent channel located. But in general the number one rule is to still cover the same area that the analog NTSC service covered before.
From an engineering point of view the system has been planned well , in my opinion , it is just the CRTC's "let the market decide aproach" what bothers me.
As usual I could be wrong though.
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| Post 17 made on Saturday October 31, 2009 at 01:43 |
Daniel Tonks Wrangler of Remotes |
Joined:
Posts: | October 1998
25,812 |
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It's hard to find examples where stations reverted to their analog channel, but it does look like the figure is less than 25%.
Buffalo:
WNYB (26 -> 26) is covering a SLIGHTLY larger footprint than analog at 4.7% power, and will be somewhat larger at 20% power.
WNYO (49 -> 49) is covering a little larger footprint at 4.0% power (less severe directionality).
Rochester:
WHAM (13 -> 13) is covering the exact same footprint at 3.3%.
WHEC (10 -> 10) is covering a little larger at 5.7%.
Erie:
WICU (12 -> 12) is covering a moderately smaller footprint at 1.7%.
WJET (24 -> 24) is covering a significantly larger footprint at 47%.
Based on that I'd hazard that most of the Canadian stations will be increasing their official range by a moderate amount, however CFTO is definitely going smaller.
Intresting tidbit: WNED with 156kW digital on channel 43 is exactly the same effective broadcast radius as 2510kW analog on channel 17.
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| Post 18 made on Saturday October 31, 2009 at 10:24 |
hd fan Regular Member |
Joined:
Posts: | March 2006
270 |
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My calculations only take into consideration free space losses and assume a flat perfect terrain for both services on the same frecuency. Real life scenarios, like the ones , IC and FCC engineers have to calculate , take into consideration other factos like the terrain that among other problems introduce multipath interference and therefore increase the noise level. The 1% is just the theoretical limit for ideal conditions. Therefore to match somehow the same coverage area the actual EIRP value is higher than 1%. I remember when FCC publicized the coverage area and data for their ATSC transmitters [Link: fcc.gov] as a general rule I noticed that the power level went down to less than 10% of what they were before but obviously not every station stays on the same frecuency and most go to a higher one. That is why I had 10% as a general rule for any station. This method of calculation (used by FCC) is theoretical and as such assume the viewer will use an outdoor antenna 10 m above ground level. But as you can see most stations acctually gain new viewers by expanding the coverage area a bit.
We are off topic , but I remember there was a website linked or from Industry Canada that has the coverage maps and data for the canadian stations but I cant find it now. I remember it was posted in this forum.
The FCC even mandated that stations loosing 2% or more of the population of the previous Analog coverage should inform their viwers daily via PSA's and created a list of 402 stations that are requiere to do so, out of a total of 1749 Full power Stations. So only 23% of all stations are going to loose 2% or more viewers.
I would assume that similar rules are being used/implemented in Canada but we are still away from the August 2011 deadline.
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| Post 19 made on Sunday November 1, 2009 at 12:17 |
hd fan Regular Member |
Joined:
Posts: | March 2006
270 |
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Just a correction after reading more not only on the ATSC.org website but also from other online sources.
The ATSC on one of their guidelines papers says:
For the same approximate coverage as an analog transmitter (at the same frequency), the average power of the DTV signal is on the order of 12 dB less than the analog peak sync power (when operating on the same frequency).
In this case then the EIRP levels could be reduced to only 6.5% of the previous analog service using the same frecuency to still cover the same area. Maybe this 12 dB number from the ATSC takes into consideration average real life scenarios such as multipath , impulsive noise and some other types of interference. As a matter of fact 2 stations from Los Angeles (Ch 11 & 13) who like CTV went back to VHF reduced power from 161 to 13 kW, in other words 11 dB reduction or almost 8%. Some other stations in New York city are actually asking to increase power to 100 kW apparently after seeing the poor results due to heavy multipath probably (lots of high raise buildings)
After reading all this I beleive that CFTO with 2.4 kW (0.9%) will actually loose significant coverage when compared with the Analog coverage. I think I have found the calculation methods or propagation models for DTV signals in NA , although maybe an early version not currently updated, so I wll recalculate this and evaluate the results.
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| Post 20 made on Sunday November 1, 2009 at 17:43 |
Daniel Tonks Wrangler of Remotes |
Joined:
Posts: | October 1998
25,812 |
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Considering that CTV is pretty much the biggest national network (at least for popularity) it's rather surprising how they're dropping the ball on power in their largest market.
Or is it. :-)
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| Post 21 made on Sunday November 1, 2009 at 18:21 |
Anthony Ultimate Member |
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Posts: | May 2001
23,965 |
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don't know if anyone is interested but there will be something on this at Canada AM tomorrow morning.
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| Post 22 made on Sunday November 1, 2009 at 19:02 |
hd fan Regular Member |
Joined:
Posts: | March 2006
270 |
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Thanks for the heads up Anthony. Will certainly record it tomorrow.
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